The present invention resides generally in the field of polymers of vinylpyridines. More particularly, the present invention relates to certain unique linear polyvinylpyridines and expedient methods for their preparation.
Linear polyvinylpyridines and functionalized derivatives and copolymers thereof are useful in a large number of applications. For instance, conductive polymers prepared from linear polyvinylpyridine and molecular iodine have been utilized as cathode materials in small solid-state batteries in which long life under low current strain is required, such as batteries used in implantable cardiac pacemakers. See, U.S. Pat. Nos. 3,660,163 (1972) and 3,773,557 (1973). Quaternary salts of polyvinylpyridines (e.g. poly(1-alkylvinylpyridinium halides)) have proven to be good negative electron beam resists for microlithography. See, K. I. Lee et al., Proc. SPIE Int. Soc. Opt. Eng., 333, 15 (1982).
Polyvinylpyridines have been used extensively in the repographic and lithographic fields because of the combination of properties ranging from adhesive to electrical properties. See, U.S. Pat. Nos. 4,041,204 (1977); 3,942,988 (1976); Ger. Offen. 3,040,047 (1981); Japan KOKAI 76 30,741 (1976); U.S. Pat. No. 4,032,339 (1977); Ger. Offen. 2,701,144 (1977); and Japan KOKAI 75 124,648 (1975). Polyvinylpyridines have also found applications in the film and photographic area. For example, solutions of polyvinylpyridine or their quaternary salts form thin films that protect the image surface of instant film prints. See, U.S. Pat. Nos. 2,874,045 (1959); 2,830,900 (1958); and 3,459,580 (1969) .
Polyvinylpyridines are compatible with synthetic and natural polymers such as polyolefins (including polypropylene), polyethylene terephthalate, nylon, and cellulose, and thus field applications in plastics, alloys and blends. Fibers incorporating polyvinylpyridines show excellent dyeing intensity and are color fast [see, e.g. U.S. Pat. No. 3,361,843 (1968)] and polyvinylpyridiniumphosphate imparts permanent fire retardancy to cellulose textiles [see U.S. Pat. No. 2,992,942 (1961)] and thus polyvinylpyridines find uses in the textile industry as well.
Polyvinylpyridines further find utility in the treatment of bleached Kraft paper to increase titanium dioxide retention in pulp slurries, and electroplating applications (in particular quaternary salts), as corrosion inhibitors for metals including iron, aluminium, copper, brass, magnesium and solders, as polymerization inhibitors in Li/TIS.sub.2 current-producing electrochemical cells, as emulsion stabilizers and dispersing agents (in particular acid salt and quaternary salt forms), as flocculating agents (particularly acid salt and quaternary ethylhalide forms), in ion exchange membrane preparation and many other applications. These and other uses for linear polyvinylpyridines are reviewed extensively in product literature available from Reilly Industries, Inc., Indianapolis, Ind. U.S.A., entitled "Linear Polyvinylpyridine: Properties and Applications" (1983 and 1989), to which reference can be made for additional information.
As to their preparation, linear polyvinylpyridines have been prepared by various general polymerization techniques. These have included radiation initiated, Ziegler-Natta initiated, free radical initiated and anionic initiated polymerizations. Radiation initiated polymerizations have usually been used for the preparation of graft copolymers. Ziegler-Natta initiated systems usually do not work well for the vinylpyridine systems.
Free radical (addition) polymerizations of vinylpyridines are common in the literature. They are carried out using initiators such as benzoyl peroxide, cummene hydroperoxide and azobis (isobutyronitrile). These polymerizations may be carried out in solution, emulsion or bulk. Free radical initiated polymerizations in alcoholic solvents are the most common for vinylpyridines. However, it is often difficult to control the molecular weight of the vinylpyridine polymers using free radical initiators. Isolation of the vinylpyridine polymers can also be difficult if the polymerization is carried out in a solvent in which the polymer is soluble.
Generally, anionic polymerizations of vinylpyridines are also common in the literature. The most common reported catalyst for anionic polymerizations of vinylpyridines is n-butyllithium. Polymerizations using such reagents are carried out in non-proton donating (non-protic) solvents such as tetrahydrofuran (THF). Historically, anionic polymerizations of vinylpyridines have been somewhat difficult to control, making it complicated to obtain linear polyvinylpyridines of desired molecular weights, especially at lower molecular weights. One known method for obtaining lower molecular weight polyvinylpyridine homopolymers is to use a large amount of catalyst relative to the amount of vinylpyridine monomer. However, this method is disadvantageous in that the use of large amounts of catalysts is expensive.
Further, when anionic and free radical polymerization catalysts are used to prepare linear polyvinylpyridines, the organic residue of the catalyst ends up as the terminal group of the polyvinylpyridine. Thus, using the conventional anionic and free radical polymerization catalysts of the prior art, the polymer end groups chemically differ from the pendant pyridyl functions of the polymer. This may modify the properties of the polymer and may also interfere with or form undesirable, potentially toxic groups, when the polyvinylpyridine polymer is derivatized to useful non-free base forms.
In light of the background in this area, there is a need for a new polymerization process which enables the efficient preparation of linear polyvinylpyridines, including the preparation of relatively low molecular weight linear polyvinylpyridines without the need for using large amounts of catalyst. Desirably, the polymerization process would provide a linear polyvinylpyridine free from non-homogeneous end groups which may impart undesirable properties to the polymer. The present invention addresses these needs.